Apparatus for making multicellular glass



Sept. 9, 1941.

ori inal Filed Nov. 5, 1937 s. L. wlLLis APPARATUS FOR MAKINGMULTICELLULAR GLASS IN V EN TOR.

JIM/FORD L. l/uua whim A TTORNEYS.

p 9, 1- s. L. WILLIS 2,255,237

APPARATUS FOR MAKING MULTICELLULAR GLASS Original Filed Nov. 5, 1937 '2Sheets-Sheet 2 III AV/y

INVENTOR. fl/IFUIED Lair 1441s A TTORNEYS.

Patented Sept. 9, 1941 UNITED STATES PATENT OFFICE APPARATUS FOR MAKINGMULTI- CELLULAR GLASS W Sanford L. Willis, White Plains, N. Y., assignorto Corning Glass Works, Corning, N. Y., a corporation of New York 7Claims.

during melting of the glass or fabrication of the article, dependingupon the time and tempera-v ture of heating, with consequent variationin cell structure.

It is the object of this invention to produce multicellular glassarticles of uniform cell structure.

' The above and other objects may beaccomplished by practicing myinvention, which embodies among its features heating granular orpulverized glass under fluid pressure to sinter the glass particles andentrap'compressed interstitial 2 air or other gas, thereby producingafrit con-'- taining compressed gas bubbles, further heating the frittedmass to sufficierltly soften the glass I and reducing the fluid pressure.to cause expan- Fig. 1 is an elevation mostly in section of a apparatusfor sintering granular or pulverized glass under pressure in accordancewith my invention;

Fig. 2 is an elevation partly in section of an apparatus forcontinuously sintering granular or pulverized glass under pressure andthereafter expanding it in accordance with my invention;

Fig. 3 is a sectional view on the line 33 of Fig. 2 showing a feedingmeans;

I Fig. 4 is a sectional view of a modification of the feeding means ofFig. 3 showing a multiple screw feed:

Fig. 5 is a detail perspective view of the orifice of the apparatusshown in Fig. 2;

Fig. 6 is a vertical sectional view of a modified portion of theapparatus shown in Fig. 2;

Fig. 7 is a detail perspective view of the orifice of the apparatusshown in Fig. 5; and

Fig. 8 is a sectional view of a modified form of feeding mechanism andsintering tube.

In Fig. '1 a sintering tube l0, whichin the present instance has acircular cross section but which may have any desired cross sectionalform, contains granular or pulverized glass II to be fritted and isrigidly attached to a movable base l2. One end of the tube I0 is closedby a cap l3 while the opposite end is provided with a stufling box l4through which passes a rod l5. Within the tube 10 the inner end of therod I5 is attached to a piston l6 and its outer end is provided with ahand wheel H. The outer ,portion of the rod I5 is threaded and passesthrough a feed block I8 which is also attached to the base ign of t 1 Incertain instanees th pul- I2. Rotation of the hand wheel I! will thusadverized'glass may be confined with or without vance the P st l5 W thinthe tube 0. An inlet additional mechanical pressure during the initial 9is provi d f admiss n f mpr ssed air or heating. Likewise finely dividedmaterial may other suitable gas.

- be mixed with the pulverized glass which, on Positioned in front ofthe tube to is a sintering heating, will decompose or react to provideadfurnace 20 which is divided into two chambers 2| ditional gas .withinthe fritted mass to cause its and 22 and is provided with burners 23 andvents expansion. I 24 for the escape of combustion products. The

The invention of the present application rechamber 2| is provided with aside port 25 for sides in various novel features of the processes ins tof the tube While Chamber 22 is p and apparatus described and claimedherein. vided with a port 26 for entrance of the extruded The majorportion of the apparatus used in pracfrit, a shelf 21 to receive thefrit and a door 28 ticing these processes and certain of the processesto permit its removal from the kiln. themselves are fully disclosed inmy co-pending n 2 a sintering tube 29 containing anuapplication SerialNumber 173,018, filed Novemlar or pulverized glass 30 is provided with afeed her 5, 1937, of which this application is a con- S ew 3| the Shaftf which Passes through a tinuation. The features of these processes willstufling box 32 and is driven by a motor and rebe more fully apparentwhen considered in conduction gears (not 1 Alternatively a p ujunctionwith the operation of the apparatus 11- ality-Qi eed Screws 35,4md 36may be emlustratedin the accompanying drawings in V ployed, as shown inFig. 4 in which the screws 33 which: 1 and 35 are threaded in one sense,for example,

left handed, and the screws 34 and 36 are threaded in the oppositesense. The right and left handed screws are rotated in alternatedirections. Obviously a piston may be. employed in lieu of the feedscrews or Figs. 3 and 4 a shown in Fig. 8 in which event the piston maypossess any desired cross sectional shape to conform with thegeneralcross sectional shape of the sintering tube, that is, circular orrectangular. The tube 29 extends into and through a sintering furnace 31and its end is drawn down and spread to form a rectangular orifice 38asshown in Fig. 5, the cross sectional area of which is substantiallyequal to that of the sinteringtube 29, but may be less as will appear.Adjoining the sintering furnace and communicating therewith is a kiln 39which forms the hot end of an annealing lehr 40. A fritted mass of glass4| within the tube 29 extends through and from the orifice 38 into thekiln 39 and expands to form a cellular frit 42 which is received on aconveyor 43 moving through the kiln 39 and the lehr 49.

The glass may be fed to the sintering tube in any suitable or desiredmanner. For the purpose of illustration an arrangement for introducingseparate chargesintermittently will be described. On top of the tube 29and communicating therewith, as shown in Figs. 2 and 3, is a verticalhopper comprising a lower chamber 44 which is provided with a compressedair or gas inlet 45, a middle chamber or air lock 45 which is alsoprovided with a compressed air or gas inlet 41 and an upper chamber 45which is open at its top for receiving a supply of granular orpulverized glass 49. A cone 50 separates the chamber 44 from the airlock chamber 45 and another cone separates the air lock 45 from theupper chamber 48. A shaft 52 which is attached .to the cone 50 and isadapted to raise and lower it, passes upwardly through a-hollow shaft53' which is attached to the cone 5| for the purpose of raising andlowering the cone 5|. At its upper end the shaft 52 passes through asupport 54 and is provided with a pressure actuated handle 55 whichoperates against a spring 55. The upper end of the shaft 53, which isspirally threaded, passes through a support 51 and is provided with ahand wheel 58 which is interiorly threaded to coincide with the threadedshaft 53, and which is adapted on being revolved to raise and lower theshaft.

In Fig. 6 a sintering tube 59 extending through a sintering furnace 50is supplied with pulverized glass 5| by means of a screw feed 52 andcom'- pressed air in themanner shown and described above for Fig. 2. Thetube 59 is provided with an orifice 53 and I an intercommunicatingexpansion chamber 54, connected therewith as shown in detail in Fig.-'7. The expansion chamber 54 extends through a kiln 55 whichforms thehot end of a lehr 55. A fritted mass of glass 51 extends through theorifice 53 and is expanded to form a cellular'frit 58 which fills theexpansion chamber 54 and upon emergingtherefromis received upon aconveyor 59. In Fig. 8 is shown a modification of the sinteringapparatus of Fig. 2. In this structure the cation a piston 12 issubstituted for the feeding screws of the other modifications and isgiven a reciprocating movement by means of a connecting rod 13operatively attached to crank pin 14 adjustably mounted in a radial slotin the rotatable drive plate I5. A stufiing box 11 prevents loss offluid pressure around the piston rod 18. The piston 12 may be operatedwith a short stroke and corresponding higher frequency. In view of theeffects of the fluid pressure in feeding the material the arrangementmaybe such that thedischarge of glass will be sintering tube. 10 isprovided-witha refractory= melting point non-metallic material providedit.

can be' made with a suflicientl'ysmooth surface so as to permit movementof the charge under the pressure of the feeding mechanism. If suchmaterials, as the electrocast refractories or the burned clay productsresult in too great adhesion "with the charge, a graphite lining may beused which isnot wetby glass. In this same modifisubstantiallycontinuous. Alternatively, the stroke of the piston may be long and lessfre-, quent and it may be operated to discharge successive unit masses,each of which is cutoff as it is extruded. In the latter case the pistonis particularly effective to confine the granular glass while it isbeing heated, applying more or less mechanical pressure as is desired.The piston head may be chilled to prevent sticking of the glass, orsticking may be sufficiently prevented by forming the operative face ofgraphite.

In practicing my invention a quantity of granular or pulverized glass IIis introduced into the tube [0 which is closed with the cap [3, thepiston I5 is advanced by turning the hand wheel 11 so as to bring thepowdered glass under a slight mechanical pressure and compressed air isadmitted thru the inlet [9 to maintain a pressure of about fifty to onehundred pounds per square inch within the tube and thruout the mass ofpulverized glass. The piston l5, being not entirely air-tight, will notinterfere with the passage of air to the forward part of the tube. Theassembly on its base I2 is then advanced until the tube I0 is insertedwithin the chamber 2| of the furnace 25 and the temperature bfthe J tubeis maintained at the sintering point of the pulverized glass until thelatter has sintered sufficiently to seal the end of the tube It. Thetube is then withdrawn from the furnace and the cap I3 is removed afterwhich the tube is reinserted so that its end registers with the port 25of the chamber 22. The piston I5 is then advanced at a rate sufficienttogether with the air pressure in the tube to extrude the sin-. teredmass from the forward end of the tube II! but not too fast to preventcomplete sintering of the granular or powdered glass as it passesthrough the heated portion of the tube. The air pressure is maintainedduring the entire operation and as a result a viscous sintered mass ofglass containing countless cells or bubbles of compressed air will beextruded from the end of the tube IN and will be deposited upon theshelf 21 in the chamber 22. The temperature of the chamber 22 ismaintained somewhat higher than that of the chamber 2| to further reducethe viscosity of the glass and cause air entrapped therein to expandandincrease the size of the I cells contained in the finished product. Theexpanded cellular fritis subsequently removed from .the chamber 22 andmay be annealed in the tained will depend upon the softening point ofthe glass employed and hence upon its composition. Practically any glasscomposition can be employed in my process, but it is preferable touseagla'ss having a relatively low softening point and a moderatetemperature-viscosity range. In most instances it will be founddesirable to employ temperatures of about 1100 F. in

' tube 29.

bricks, blocks and the like, or for the production of sheets and otherlarge articles of multicellular glass. In this case the pulverized glass30 is fed continuously into and through the extrusion or sintering tube29 by means of the feed screw 3| and compressed air. A supply ofpulverized glass is maintained in the chamber 44 and compressed air,admitted at the inlet 45, permeates and fills the interstices betweenthe glass particles in the For the purpose of replenishing the supply ofpulverized glass in the chamber 44, the fresh quantity 49 is introducedinto the air lock chamber 46 by lowering the cone 5! after which thecone is returned to its seat to seal the chamber 46 against the outsideair. Compressed air is then admitted to the chamber 46 thru the inlet41, preferably-at a pressure slightly in excess of that maintained inthe chamber 44 and the cone 5B is then lowered by operation of thehandle 55. This permits the charge of pulverized glass to enter thechamber 44 without loss of the air pressure therein. After thepulverized glass has been discharged from the chamber 46, the cone 50 isreturned to its seat and the chamber 46 is sealed from the chamber 44.Before a fresh charge of pulverized glass is introduced into the chamber46 from the chamber 48, the air pressure in the chamber 46 preferably isreleased thru the inlet 41, thereby avoiding a blow-back when the cone5| is again lowered.

As the pulverized glass 30 under the influence of the mechanical andfluid pressure is moved forward thru that portion of the extrusion tube29 which is within the furnace 31, it is heated sufliciently to causethe glass particles to sinter and coalesce and entrap the air in theinterstices thereof, thereby forming the viscous fritted mass 4|containing countless bubbles of compressed air. The frit 4| is forcedcontinuously thru the orifice 38 into the kiln 39 and upon the conveyor43. The temperature of the kiln 39, as pointed. out above, is somewhathigher than the temperature of the sintering furnace 31 and under theinfluence of this increased temperature the viscosity of the frit 4| isreduced and the compressed air bubbles entrapped therein expand therebyforming the xpanded frit 42 with a uniform cellular structure. Theconveyor 43 continuously carries the expanded frit 42 into the annealinglehr 40 where it is slowly cooled in the usual manner after which it maybe cut into blocks or sheets of convenient size by sawing or grinding orboth. I

The expansion of the fritted mass 4| by the method described above isunconfined and free before, it passes thru the expansion chamber 64which maintains it to the desired dimensions when it expands during itstravel thru the kiln desired mechanical pressure at the 65. Expansionmay take place transversely of the extruded frit or it may be caused tooccur longitudinally thereof by speeding up the rateof flow in theexpansion chamber. In the latter event the expansion chamber may havesubstantially the same cross section as the orifice. Upon issuing fromthe expansion chamber into the lehr 66 and upon conveyor 69, theexpanded frit 68 will have acquired the dimensions of the expansionchamber,

The sintering tube of the embodiment illustrated is shown as horizontal.Certain advantages are obtained if the tube is positioned verticallyproviding certain features of a column. The weight of the glass willthen have an effect, positive or negative, on the resistance toextrusion modifying the degree of choke necessary. If in such column themass is fed downward the weight of the superimposed unconsolidatedmaterial above the sintering zone may provide the sintering zone.

Other advantages may be obtained-by feeding the charge upward in thevertical column. .The weight of the column of material above thesintering zone will not necessarily add to the mechanical pressurecompacting the glass at the sintering zone. The arrangements may be suchthat the air pressure predominates almost exclusively as the feedingforce to feed and extrude the molten glass while the mechanical pressuremerely holds the glass particles in place with. as

little pressure as desired. For some products it may be desirable evento release the mechanical pressure to permit the formation of largevoids or weakened portions in the ribbon'of glass.

'It is a feature of the process herein describedthat provision is madefor causing substantially equal amounts of air or other gas to beentrapped within the diiferent zones of the sintering mass. If aquantity of pulverized glass resting on an impervious, non-poroussupport is heated in a mufiie while maintaining normal atmosphericpressure within the muflie, the mass will fuse on the surface and willbe cemented to the support at the edge and, as the heat penetratesinward,

to proceed to a maximum. It may be desirable to confine the mass duringexpansion or limit the thickness of the expanded frit in order to obtaina uniformly thick product with vitreous surfaces. This can be done bypassing the expanded frit 42 between rolls (not shown) while it is stillsoft enough to be shaped but is preferably accomplished by means of themodified apparatus shown in Fig. 6. The fritted mass 61 is formed andextruded from the orifice 63 in the manner described above for Fig. 2.However,

instead of being permitted to expand freely as the expanded air willmigrate inward while the successive zones fuse entrapping .a proportionof the air. However, the migration of the air will bring about 'acondition wherein at the center there is a very considerably greateramount of air in proportion to theground glass. The result of this isthat a blow hole forms toward the center and makes it impossible toobtain a uniform cell structure. The position of the blow hole in themass, its shape, etc., differs with various conditions. In some casesthe final expanded finished mass is flat on the bottom with themigrating air will escape through the porous.

support with the result that while the total expansion of the mass isnot as great,'the cell structure of the mass is substantially uniformand shows no blow holes or deformation of the bottom of the cake.

From the above it is evident that it is desirable to provide forbleedingout the excess portion of the gas during the progressive heating inorder to obtain an equalization of pressure.

In the continuous process described to illus- -trate the principles ofthe present invention, the

bleeding of the excess gas or air and the maintenance of equal gaspressures at the zone of sintering is maintained by heating the glassmass from the sides while leaving open communication to the rear thruthe moving mass.

In the practice of my invention the following elements should beconsidered:

Grain size-Voids within granular aggregates depend upon close sizing ofthe grains rather than upon their average size. In fact, with all grainsize down to but excepting a fine dust, the percentage of voids willremain practically constant, if the material is closely sized. Thepercentage of voids can be decreased materially thru inclusion withinthe mass of a percentage of grains substantially finer than the mainbody of the mass, or thru the use of a wide range of sizes, the decreasebeing due to the tendency of the fines to fill the interstices betweenthe larger grains. Other factors remaining constant, the use of finergrained material will result in the formation of more and smaller cellsgiving a lighter material than with the larger grain batch. If the fritbe ground so that a substantial part is of two hundredmesh or finer theresultant product for a given operating pressure becomes materiallylighter than that produced with coarser grained batch, all out ofproportion to what would normally be expected from the difference ingrain size.

The term ,granular glass as used in the specification and claims isintended to include both the coarser and the most finely pulverizedparticles of glass which when fused and expanded will give a porousglass product.

Mechanical pressure.The function of the mechanical pressure, such asthat exerted by the feeding devices described above, is to hold theglass particles in contact so as to facilitate heat specific gravity ofthe final product depends on the ultimate expansion of the gas cellstherein which in turn depends on the amount of gas in the mixture and.its pressure during the sintering operation.

Since compressed air is readily obtainable and relatively constantpressures can easily be created and maintained with it, I commonlyutilize this material as the means for exerting fiuid pressure in theabove described process. If all of the grains of glass are substantiallyequal in size and especially if they are very fine the total percentageof voids in the frlt is relatively large and a lower air pressure can beused to produce a given porosity. On the other hand, if a wide range ofgrain sizes and high mechanical pressures are used resulting in a low prcentage of voids in the frit, a higher pressure will be used to producethe same porosity in the final product.

While the simple introduction of inert gas under pressure gives asatisfactory performance of my process and a desirable product, thereare certain advantages to be obtained by providing for the evolution orgeneration of gas within the mass during the heating operation,especially if ticles fuse together or in the subsequent heatingpenetration, inhibit air migration and premature expansion as the heatpenetrates the mass, and

to facilitate sintering and sealing of the cells.

For a maximum amount of occluded air, the mechanical pressure should beno higher than is necessary to accomplish the desired result. Pressureswhich are higher than necessary result in a material reduction in cellvolume of the frit, but this may be counterbalanced by the use of higherair pressuresas will later appear. It

' should be noted that the progress of the sintered material thru thesintering tube is due chiefly to the pressure exerted by the air. Themechanical pressure simply follows up the progress of the material,holding the grains in place during sintering and will constitute only avery small part'of the total driving force. In fact, when operations areconducted on a batch basis, as distinguished from continuous operation,mechanical pressure may be eliminated entirely and blocks of foamedglass may be formed in open topped molds, the atmosphere about thepowdered charge of glass being compressed during heating andsubsequently reduced.

Fluid pressura-Any gas which has no objectionable effect on theapparatus or the final product may be employed as the means for ex- Lilof the mass.

In a preferred modification finely divided carbon, preferably vegetablecarbon as distinguished from carbon produced from bone or mineral oils,may be added to the powdered glass and superheated steam used as thefluid pressure material. At about the sintering temperature of the glassthe carbon and steam react quantitatively to form hydrogen and carbonmonoxide thus producing two volumes of gas for each volume of steamintroduced. Similarly, if carbon dioxide gas be introduced under pressure as the fluid pressure medium, a reaction will be obtained at aboutthe sintering temperature of the glass by which two volumes of carbonmonoxide are formed for each volume of carbo dioxide introduced.

In another modification it has been found desirable to mix with theglass a. small amount of finely divided zinc or even zinc oxide, as wellas a moderat amount of carbon. In this case air is again used as thefluid pressure medium. When the mixture is raised to the sinteringtemperature of the glass the oxygen of the air combines with some of thecarbon rather than with the zinc while any excess carbon tends to reducethe zinc oxide if it has been included in the mix. Thus, as the glasssinters some carbondioxide is formed and the metallic zinc vaporizes,

', both combining with the gas already present in As the glass is raisedto sintering temthe escape of any of the evolved gases and products ofcombustion the result is to raise the pressure within the mass in thesintering tube thereby effecting a higher pressure within the cells ofthe sintered mass than would result merely from the originalintroduction of the fluid under pressure. This is not only an easymethod of increasing the expansibility'of the sintered mass, but alsofills the cells of the final article with a vapor which may have a lowerheat conductivity than would be the case with air alone. Furthermore,when a metal vapor is present it condenses on cooling as a mirrorcoating on the cell walls thereby lowering the conductivity of the massto radiant heat. In all of these cases the additional pressure developedby the evolution and generation of gases augments the original fluidpressure and tends to increase the rate of movement of the sintered massthru the tube. In a sintering tube in which the ratio of circumferenceto cross sectional area is high, the natural tendency of the viscousmass to wet and stick to practically all types of surface will sufficeto prevent excessive speed of flow, and such retardation will permit'thecomplete sintering of the mass as it passes thru the sinter-' ing tubeor furnace. On the other hand, when the ratio between circumference andcross sectional area is low, it may be desirable'further to retard thespeed of flow by means of a constriction in the sintering tube,preferably placed near the outlet orifice, or by making the crosssectional area of the orifice itself somewhat less than that of thesintering tube. In general, whether the fluid pressure is maintainedfrom outside sources or partially developed by the evolution orgeneration of gases within the sintering chamber, pressures of fromfifty to one hundred pounds per square inch will be found suitable.

Sintering temperatuTe.--As pointed out above. the sintering temperaturewill depend upon the glass composition used, but if the temperatureemployed is much higher than that necessary for sintering the powderedmaterial, it may materially reduce the amount of air entrapped, due tothe collapse of the particles during slntering and before the cells aresealed.

Eivpansion temperature-There is a definite limit to the cell expansionpossible with a given initial cell gas pressure and this limit isattained with maximum temperatures but below this the temperature ofexpansion can be used to control the expansion and the gas pressurewithin the cells of the final product. Thus if a high air feed pressureis used and the expansion temperature is maintained at a point at whichthe frit is still quite viscous, a final product will be obtained inwhich the cell gas pressure will be considerably above atmospheric, butthe specific gravity would be as low as would be obtained by the use oflower air pressures and higher expansion temperatures. Cell gaspressures above one atmosphere possess the advantage that they promoteincreased mechanical strength.

Expansion and annealing time.When the expension of the fritted mass iscarried on within the confines of an expansion chamber comprising anextension of the sintering tube, as shown in Fig. 6, the product will beextruded as fast as it expands so that the timing factor in this case isself-regulating. When on the other hand the frit is extruded into a kilnfor free and unconfined expansion, the time interval required forexpansion will materially affect the character of the product. Bestresults are obtained when the frit is heated'quickly, and removed fromthe hot zone immediately the expansion has taken place. Long soaking atthe higher temperature level causes the cells to coalesce, thus forminga large cell product. In annealing, the product should be quicklychilled to a point at which viscosity is very high and then slowlycooled through the critical range in the usual manner. 4

While in the foregoing there has been shown and described thepreferredembodiment of my invention, it is to be understood that minor.

changes in the process as described and in the details of construction,combination and arrangement of parts may be resorted to withoutdeparting from the spirit and scope of the invention as claimed.

I claim: 1. Apparatus for making multicellular glass, which includes asubstantially horizontal sintering tube having at one end an orifice andat the other end a continuous charging means comprising a screw feedingdevice within the tube, means for applying and maintaining a gas underpressure within the tube including a chamber to supply material to thescrew feeding device, an air lock chamber above the supply chamber andcommunicating therewith, a hopper above the air lock chamber andcommunicating therewith, means for optionally sealing the supply chamberfrom the air lock chamber, similar sealing means between the air lockchamber and the hopper, means for supplying compressed gas to the airlock chamber, means for heating the orifice and the adjacent portion ofthe sintering tube, and a heating kiln adjacent the orifice.

2.'Apparatus for making multicellular glass, which includes asubstantially horizontal sintering tube having at one end an orifice andat the other end a continuous charging means comprising a screw feedingdevice within the tube, a chamber to supply material to the screwfeeding device, an air lock chamber above the supply chamber andcommunicating therewith, a hopper above the air lock chamber andcommunicating therewith, means for optionally sealing the supply chamberfrom the air lock chamber, similar sealing means between the air lockchamber and the hopper, means for applying and maintaining a gaspressure within the tube including ducts for supplying compressed gas tothe supply chamber and the air lock chamber, an expansion tube joined to,and communicating with the orifice, means for heating the tubes and theorifice, and a lehr adjoining the end of the expansion tube.

3. Apparatus for making multlcellular glass, comprising a tube intowhich granular glass is charged and through which the chargeis movedwhile being heated to a sintering temperature and while being maintainedunder a gas pressure, means at one end of the tube for admittinggranular glass into the tube while maintaining gas pressure within thecharge, means for applying and maintaining a superatmospheric gaspressure within the. granular charge in the tube, means for heating thetube to sinter the glass, and means for moving the sintering chargethrough the tube, the other end of the tube having an opening for thedischarge of sintered glass which glass seals said opening against therelease of gas pressure maintained within the granular charge.

4. Apparatus for making multicellular glass.

comprising a tubeinto which granular glass is charged and through whichthe charge is moved while being heated to a sintering temperature andwhile -being maintained under a gas pressure, means'at one end of thetube for admitting granular glass into the tube while maintaining gaspressure. within the charge, means for applying and maintaining a gaspressure within the granular charge in the tube, means for heating thetube to sinter the glass, and means for moving the sintering chargethrough the tube, the other end of the tube having a restricted orificefor the discharge of sintered glass which glass seals said orificeagainst the release of gas pressure maintained within the granularcharge.

5. Apparatus for making multicellular glass, comprising a tube intowhich granular glass is charged and through which the charge is movedwhile being heated to a sintering temperature and while being maintainedunder a gas pressure, means at one end of the tube for admittinggranular glass into the tube while maintaining gas pressure within thecharge, means for applying and maintaining a gas pressure within thegranular charge in the tube, means for heating thetube to sinter theglass, and means for moving the sintering charge through the tube, theother end of the tube having an opening for the discharge of sinteredglass which glass seals said opening against the release of gas pressuremaintained within the granular charge, the tube being provided with aliner resistant to adhesion of sintered glass whereby to facilitate themovement thereof through the tube.

6. Apparatus for making multicellular glass providing a closed system,which comprises a sintering tube to receive a granular charge, means forexerting mechanical pressure to feed the granular charge longitudinallyof the tube,

means for applying and maintaining a gas pressure within the granularcharge, means for heating the tube to fuse the granular charge, and a.heating kiln to receive the extruded charge.

7. Apparatus for making multicellular glass, comprising a tube, intowhich granular glass is charged and through which the charge is movedwhile being heated to a sintering temperature and while being maintainedunder a gas pressure, said tube having a discharge orifice restricted toeffect substantially air-tight pressure sealing by the outflowing moltenglass, means for applying and maintaining a gas pressure within thegranular charge in the tube, mechanical means for feeding granular glassinto the tube while maintaining gas pressure in the charge, means forheating the tube to sinter the glass and means for moving the sinteringcharge through the tube, the tube being provided with a liner resistantto adhesion of sintered glass whereby to facilitate the movement thereofthrough the tube.

SANFORD L. WILLIS.

CERTIFICATE OF CORRECTION. Patent No. 2,255,257. September9, 19141.

SANFORD L. WILLIS.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 5,sec

0nd column, lines 25 and 26, claiml, strike out the words "means forapply.

ing and maintaining a gas under pressure within the tube including" andinsert the same after the comma and before "means" in line'fih, sameclaim;

and that the said Letters Patent 'shouldbe read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

' Signed and sealed this l en day of November; A. D. 191a.

Henry Van Arsdale, (Seal) Acting Comnis sioner of Patents.

